Effectiveness and robustness of a quasi-harmonic-type multistable nonlinear energy sink-inerter for dynamic response mitigation: theoretical, experimental, and numerical research

The practical application of conventional nonlinear energy sinks (NESs) is constrained by large mass requirements and strong sensitivity to input energy levels. This study proposes a novel quasi-harmonic-type multistable nonlinear energy sink-inerter (QH-MNESI) to effectively overcome these limitations. The device effectively integrates the multistable and quasi-harmonic characteristics of restoring force with the mass amplification effect of an inerter via a rotational mechanism. After deriving the governing equations and optimizing the parameters, the control performance is evaluated through shaking table tests on a small-scale steel frame structure. Experimental results demonstrate that under seismic excitations with PGAs of 0.2g and 0.4g, the RMS displacement ratios between all controlled structures relative to the uncontrolled ones remain below 0.5, for both normal and damaged states. Furthermore, an experimentally validated numerical model is developed to elucidate the vibration-damping mechanisms, including the hysteretic behavior, energy transfer pathways, and resonance capture capacity. Comprehensive analyses, including robustness evaluations under impulse loads and seismic analysis with 100 real records, confirm the superior adaptability of the QH-MNESI. Under impulse excitation, it achieves over 50% displacement reduction within 1 s. Under seismic conditions, it attains an effective control rate exceeding 94% for original structures and those with 20% stiffness degradation. The QH-MNESI demonstrates effective control performance and remarkable robustness against variations in structural properties and energy levels. The effectiveness is attributed to its key capabilities such as multi-stability, resonance capture, and targeted energy transfer. The work demonstrates that the QH-MNESI can provide a highly robust and effective strategy for addressing vibration challenges of diverse structures under complex loadings.